Three-terminal nonlocal conductance in Majorana nanowires: Distinguishing topological and trivial in realistic systems with disorder and inhomogeneous potential

TL;DR

This paper develops a theory for three-terminal nonlocal conductance in Majorana nanowires, assessing its effectiveness in distinguishing topological Majorana states from trivial states amidst disorder and inhomogeneity, and suggests combined measurements for conclusive identification.

Contribution

It provides a comprehensive analysis of local and nonlocal conductance in realistic Majorana nanowires, highlighting the limitations of nonlocal conductance alone and proposing combined measurements for reliable topological state detection.

Findings

Local conductance peaks are not sufficient to distinguish trivial from topological states.

Nonlocal conductance is too weak to reliably indicate topological phase transitions in disordered systems.

A combination of electrical and thermal conductance measurements is necessary for conclusive Majorana detection.

Abstract

We develop a theory for the three-terminal nonlocal conductance in Majorana nanowires as existing in the superconductor-semiconductor hybrid structures in the presence of superconducting proximity, spin-orbit coupling, and Zeeman splitting. The key question addressed is whether such nonlocal conductance can decisively distinguish between trivial and topological Majorana scenarios in the presence of chemical potential inhomogeneity and random impurity disorder. We calculate the local electrical as well as nonlocal electrical and thermal conductance of the pristine nanowire (good zero-bias conductance peaks), the nanowire in the presence of quantum dots and inhomogeneous potential (bad zero-bias conductance peaks), and the nanowire in the presence of large disorder (ugly zero-bias conductance peaks). The local conductance by itself is incapable of distinguishing the trivial states from the topological states since zero-bias conductance peaks are generic in the presence of disorder and inhomogeneous potential. The nonlocal conductance, which in principle is capable of providing the bulk gap closing and reopening information at the topological quantum phase transition, is found to be far too weak in magnitude to be particularly useful in the presence of disorder and inhomogeneous potential. Therefore, we focus on the question of whether the combination of the local, nonlocal electrical, and thermal conductance can separate the good, bad, and ugly zero-bias conductance peaks in finite-length wires. Our paper aims to provide a guide to future experiments, and we conclude that a combination of all three measurements would be necessary for a decisive demonstration of topological Majorana zero modes in nanowires -- positive signals corresponding to just one kind of measurements are likely to be false positives arising from disorder and inhomogeneous potential.